install gnuplot for test

Author: JacobBarthelmeh

.github/workflows/sftp-benchmark.yml

@@ -90,6 +90,9 @@ jobs:
           path: ./wolfssh/
           artifact_id: 'openssh-download'
 
+      - name: Install gnuplot
+        run: sudo apt-get install gnuplot
+
       - name: Setup OpenSSH Test Server
         working-directory: ./wolfssh/
         run: |